Floristic Diversity and Conservation Value of Tanoe-Ehy Forest in South-Eastern (Cote d'Ivoire)
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European Scientific Journal July 2018 edition Vol.14, No.21 ISSN: 1857 – 7881 (Print) e - ISSN 1857- 7431
Floristic Diversity and Conservation Value of
Tanoe-Ehy Forest in South-Eastern (Cote d’Ivoire)
Missa Koffi
Ouattara Noufou Doudjo
Bakayoko Adama
University Nangui Abrogoua, UFR Sciences de la Nature, Abidjan, Côte
d'Ivoire, Swiss Center for Scientific Research in Côte d'Ivoire
Doi: 10.19044/esj.2018.v14n21p61 URL:http://dx.doi.org/10.19044/esj.2018.v14n21p61
Abstract
The Tanoe-Ehy Forest, located in the South-Eastern of the Côte
d’Ivoire is one of the rare forest cover of this type that still exists in the
Country. These Forest was identified as a top priority site for conservation in
West Africa. However, this important forest is subject to strong
anthropogenic pressures which through poaching, uncontrolled takeoffs of
natural resources and some agricultural clearing. A Botanical study based on
plots, itinerant and linear inventory conducted in this forest intends to assess
the plant species diversity and the conservation value for biodiversity of this
forest. At the end of the study, 432 plant species were recorded. Among them,
14 are listed on endemic of Upper Guinea and 16 threatened and endangered
list of species. Concerning the species threatened and endangering, 3 species
are really in endangering (Hemandradenia chevalieri, Tieghemella heckelii,
Irvingia gabonensis) and 13 others are a category of vulnerable species. A
Sassandrian species of type II (Piptostigma fugax) was also observed. The
dominant species of the forest are Symphonia globulifera and Uapaca
paludosa. Concerning the vegetation condition, the swamp forest, the dry
land forest and the raphiale vegetation have a high conservation value.
Keywords: Diversity, endemic, endangered, Côte d'Ivoire.
Introduction
In Côte d’Ivoire, the rate of deforestation is one of the highest in the
world, it is estimated to 6,5 % (Myer, 1989). If the development of cocoa and
coffee cultures is responsible for the disappearance of dry land forest. It is
rather of the banana and oil palm crops that have contributed to the reduction
of swamp forests. Vast areas of this type of forestry training have been
transformed into large plantation of banana tree and oil palm by mighty
61European Scientific Journal July 2018 edition Vol.14, No.21 ISSN: 1857 – 7881 (Print) e - ISSN 1857- 7431
agricultural societies. This has involved the rarity of this type of vegetation
formation in the rural domain (Kouamé, 2012).
The Tanoé-Ehy Forest is located in the South-Eastern of the Côte
d’Ivoire is one of the rare forestry formations of this type to exist. This swamp
forest is located at the interface of the Tanoé river and Ehy lagoon. The first
multidisciplinary investigations, in primatology, socio-anthropology,
ichthyology, in ornithology, have demonstrated the exceptional character of
these forests by its wealth and its diversity faunic. Because of the presence of
some threatened species, this forest has been identified as a high value site for
conservation (Koné et al., 2008). However from the floristic point of view no
study has shown its conservation value. This forest is threatened by the harvest
of medical plants, heat-seeking wood and by the palm-ci, a powerful
agricultural society in research of Marshland for extension of its oil palm
plantations (Zadou et al., 2011).A sustainable management of this vegetation
formation turns out so indispensable for its survival. This goes by knowledge
of its biodiversity also animal as floristic. The inventory conducted in this
forest intends to characterize the floristic and structural aspect. In order to
determine the conservation value for biodiversity of this forest.
Methodology
Study site
The Tanoé-Ehy Forest (approximately 12,000ha) is an unprotected
forest in south-eastern Côte d’Ivoire, at the boarder of Ghana, between the
latitudes 5°05’ and 5°15’ and the longitudes 2°45’ and 2°53’ (Figure1). The
land is owned by all the villages surrounding the forest and each of these
communities hold native rights to exploit the forest. It is located in the Ivorian
littoral sector. She covers a superficies of 12000 ha.
The climate of the region, which is a sub-equatorial type comprise 4
seasons (Avenard etal.,1971; Lauginie, 2007) a great rainy season (end of
April to half July) and one dry season (from December to April) alternating
with one short rainy season (from half September to the end of November) and
one small dry season (half, July-half, September).
The study area is characterized by the one of the Guinean domain
(littoral sector). This forest is rich of species from lagoons and avifauna
species of swamping ecosystems (Goliath, heron, eagle fisher, etc.). This
fauna is adapted to the swampy conditions of the area, which protect it. The
habitat decreases with increasing area of industrial plantations some primates
(Cercopithecus Diana roloway Von Schreber, 1774, Cercopitheques
campbelli Thomas, 1923 and Colobus velleosus Geoffroy Saint Hilaire, 1834
are also found in the forest.
62European Scientific Journal July 2018 edition Vol.14, No.21 ISSN: 1857 – 7881 (Print) e - ISSN 1857- 7431
Field method
For the collect of data, we chose the linear method of Gautier et al..
(1994). This method had been already used, for several studies in tropical
forests (Bakayoko et al., 2001; Chatelain, 1996; Kouamé et al., 1998). The
method consists in counting all the points of contact of the vegetation along
an imaginary vertical line, placed in an equidistant way along a graduated
ribbon. The standard length of transect is 200 meters. Because of the nature
and humidity of soils observed in swamp areas where it is difficult to move
without sinking and the small size of the dry land forests we have used a length
of 100 meters. In these forests, measurement is made each 1 meter. The
minimal and maximum height of each contact with the vegetation is measured
using a stake of 8 meters. This stake is drawn up vertically. The values beyond
8 meters heights are estimated. For each contact, the species and the distance
to which each individual is met on transect are noted.
The plot method was usually use for forest inventories in tropical zone
(Spichiger et al., 1996; Hawthorne, 1996; Adou Yao et al., 2007).In order to
record a maximum representative species of the inventory zone, for the study,
the Tanoé-Ehy Forest has been divided into 110 squares of 20 m by side. The
position (altitude/longitude) of each plot was recorded by a GPS. In each plot
all vascular plant species (trees, shrubs, grass, and lianas) were recorded. A
sub-plot of 10 m2was selected in which, some details data were recorded (DBH
individuals numbers) for individuals with diameter equal or more than 5 cm at
1m 30 high. To get a more accurate estimation of species richness and
composition, additional species were added thanks to itinerant prospection.
63European Scientific Journal July 2018 edition Vol.14, No.21 ISSN: 1857 – 7881 (Print) e - ISSN 1857- 7431
Figure I: Map of Tanoé-Ehy area, the geographical framework of this study
Data analysis
After establishing, species were examined to identify and count
endemics, referring to previously checklist established by Poorter et al.
(2004), for Upper Guinea endemic species. The list of threatened and
endangered species was established according to the IUCN checklist of
2018.In order to appraise the floristic diversity in the Tanoé -Ehy Forest and
to compare the diversity of the biotope, the Shannon (1948) diversity index
has been calculated. This index is usually used in ecological studies (Huston,
1995) as measure of heterogeneity and takes into account the regularity of
species abundance (Peet, 1974). It’s calculated as the following formula:
H = - Σ (Ni/N) x Ln (Ni/N)
Ni is individuals number for species i and N is the total numbers of all species.
In order to appraise the preponderance of species of the forest swamp of
Tanoé-Ehy flora the Importance Value Index (IVI) has been calculated. It has
been used in different tropical forest by different authors (Curtis and
McIntosh, 1951; Bakayoko, 1999 and Adou Yao et al., 2007). Importance
Value Index (IVI) was calculated for each species (i) as:
IVI = RDeni + RDomi + R Frqi.
RDeni is relative density, RDomi is relative Dominance, and RFrqi is relative
frequency of species (i).
Species richness, species with special status, density and basal area of
woody trees (> 5 cm), disturbance index, overlap, number of gaps, gap width
and regeneration rate are criteria that we have taken into account to show the
importance of this forest for the conservation of biodiversity.
To determine the conservation value of each biotope we have summed
the crosses of these criteria. The crosses symbolize scales of value for each
criteria. The sum of all the crosses being 48, we chose to vary the sum from 0
64European Scientific Journal July 2018 edition Vol.14, No.21 ISSN: 1857 – 7881 (Print) e - ISSN 1857- 7431
to 40. A biotope with the number of crosses between 0-10 at a very low value
of conservation. Between 10-20 a low conservation value, 20 and 30 an
average conservation value, between 30 and 40 a great value conservation and
more than 40 and above a very high conservation value.
To appreciate vegetation condition, gap width, and biotope recovery
were used. The recovery of each biotope was built from averages of the strata
of different survey.
Results
Floristic composition and diversity
This inventory of surface listing combined three methods (surface,
linear and itinerant) constitutes the first one implemented in Tanoé-Ehy
Forest. In total, 432 plant species have been listed in the Tanoé-Ehy Forest
according to Angiosperm Phylogeny group (APG IV, 2016). This number
shows a relatively high diversity in this forest (table 1). Among the species 51
have special status (Endemic species of Upper Guinea, of Cote d’Ivoire,
threatened and endangered). For the threatened and endangered species, 16
have been recorded in the Marsh Forest Tanoé-Ehy (table 2). Among them, 3
species are really in endangering (Hemandradenia chevalieri, Tieghemella
heckelii), 1 endangered species but with a minor concern (Irvingia
gabonensis) and 13 others are a category of vulnerable species. A Sassandrian
species of type II (Piptostigma fugax) was also observed. Concerning the IVI
of the forest. Symphonia globulifera (43.10) and Uapaca paludosa (35, 03)
have the highest IVI values (table 3).
Table 1: Shannon index and Pielou equitability
Floristic parameters Tanoé- Ehy Forest Dry land forest Swamp forest Raphiale
Shannon index 5,09 3,27±1,5 2,37±0,5 1,25±0,01
Pielou equitability 0,90 0,81±0,1 0,52±0,2 0,29±0,02
Table 2: Threatened and endangered species listed in the Tanoé-Ehy Forest according to
IUCN (2017)
Species Families Status of conservation
Anopyxis klaineana (Pierre) Engl. Rhizophoraceae VU Ald ver 2.3 (1994)
Entandrophragmacandollei Harms Meliaceae VU Ald ver 2.3 (1994)
Garcinia afzelii Engl. Clusiaceae VU Ald ver 2.3 (1994)
Guarea cedrata (A. Chev.) Pellegr. Meliaceae VU Ald ver 2.3 (1994)
Hemandradenia chevalieri Stapf Connaraceae En B1 12C
Hallea stipulosa (DC.) J.-F.Leroy Rubiaceae VU Ald ver 2.3 (1994)
Hallea ledermannii (K.Krause) Verdc. Rubiaceae VU Ald ver 2.3 (1994)
Irvingia gabonensis (Aubry Le-comte ex
Irvingiaceae LR/ nt ver2.3(1994)
O'Rorke) Baill.
Lovoa trichilioides Harms Meliaceae VU Ald ver 2.3 (1994)
Lophira alata Banks ex C.F. Gaertn. Ochnaceae VU Ald ver 2.3 (1994)
Milicia excelsa (Welm.) C.C. Berg Moraceae VU Ald ver 2.3 (1994)
65European Scientific Journal July 2018 edition Vol.14, No.21 ISSN: 1857 – 7881 (Print) e - ISSN 1857- 7431
Milicia regia (A. Chev.) C.C.Berg Moraceae VU Ald ver 2.3 (1994)
Nauclea diderrichii (De Wild. & T. Durand) VU Ald ver 2.3 (1994)
Rubiaceae
Merr.
Piptostigma fugax A.Chev.ex Hutch.Dalziel Annonaceae VU Ald ver 2.3 (1994)
Tieghemella heckelii (A. Chev.) Pierre ex A.
Sapotaceae En B1 12C
Chev.
Tarrietia utilis (Sprague) Sprague Malvaceae VU Ald ver 2.3 (1994)
Table 3: Importance Value Index of the species in the Tanoé-Ehy Forest
Relative Dominance Relative density Relative Frequency
SPECIES (%) (%) (%) IVI
Symphonia globulifera 14,91 15,11 13,08 43,10
Uapaca paludosa 13,02 12,01 10,00 35,03
Anthostema aubryanum 17,98 7,64 5,58 31,21
Tarrietia utilis 17,98 7,64 5,58 31,21
Hallea stipulosa 11,12 8,90 6,94 26,97
Xylopia rubescens 1,66 9,06 9,59 20,31
Raphia hookeri 8,12 4,20 4,16 16,48
Spondianthus preussii 4,26 6,47 4,23 14,96
Hallea ledermannii 6,86 2,43 2,71 12,00
Uapaca guinnensis 1,89 3,10 4,20 8,06
Syzygium rowlandii 0,14 1,84 1,85 4,80
Funtumia africana 0,42 1,45 1,00 2,87
Nauclea diderichii 0,06 0,98 1,76 2,81
Other 1,58 19,15 29,33 50,03
Total 100 100 100 300
Structure of vegetation
The observation of these coverings shows that at the level of the
recovery, the raphiale middle, the strate of herbaceous and small shrubs less
than two meters is very poorly occupied. Then a progressive increase of the
percentage of recovery up to the stratum 8 at 16 meters is observed. This
percentage falls at the level of the stratum. For the swamp forest, the strate
base is very covered, the vegetation is dense in medium stratum from thee
strate vegetation occupation decreases. Emerging stratum has a percentage
of over 20% (Figure 2).
Conservation value of Tanoé-Ehy Forest
Analysis of the table 4 shows that the swamp forest, the dry land forest
and the raphiale have a high conservation value. The sum of the crosses
representing the conservation value is 36; 32 and 34 respectively for marshy
forest, raphiale and land forest. The marshy forest has a high conservation
value due to the large number of species, the number of rare species according
to Aké-Assi and the number of rarity and threatened species according to
66European Scientific Journal July 2018 edition Vol.14, No.21 ISSN: 1857 – 7881 (Print) e - ISSN 1857- 7431
IUCN. Concerning the raphiale and the dry land forest. The high conservation
value observed in these biotopes is due to the low perturbation of these two
areas.
Figure 2: Recovery from the recovery stratum biotope Raphiale (A); Swamp forest (B); Dry
land forest (C)
67European Scientific Journal July 2018 edition Vol.14, No.21 ISSN: 1857 – 7881 (Print) e - ISSN 1857- 7431
Table 4: Conservation value of each recognized biotope in the Tanoé-Ehy Forest
Indicators Swamp forest Raphiale Dry land forest
Number of species xxxxx xxxx xxx
Scarce number according Ake-Assi xxxx xx xx
Number of species from Upper Guinea xxxx xxx xxxx
Number of IUCN Species (2015) xxxx xxx xxx
Number of West African endemic species xxx xxx xxx
Density xxx x xxx
Basal area xxxx xxx x
Recovery xx x xxx
Width of the gaps (15m) x xxxx xxxx
Number of holes (15m) x xx xx
Pioneer Index (PI) xxx xxxx xxx
Regeneration rate xx xx xxx
36: High 32: High 34: High
Total + Conservation Value conservation conservation conservation
value value value
Discussion
Floristic composition and diversity
Concerning our study, to have arguments to heepher, we characterized
the Tanoé-Ehy Forest generally and the various biotopes which make up her.
Confronting the results of this study with the criteria recognized by the forest
stewardship, some observations can get free. The first criterion recommend
that the forest is to be protected. The Tanoé-Ehy Forest satisfied this criterion
because the first ones measures of its protection were already taken. Then, the
concept requires a concentration of vulnerable species, in or danger or
threatened. The analyze of the general flora indicates that the Tanoé-Ehy
Forest includes fifty-one botanical species with particular status. This
proportion is superior for example to thirty-four botanical species with
particular status for the forest of the site of the intended voluntary nature
reserve.Among these species with particular status, we observe the presence
of the endemic species, the botanical species rare and threatened according to
Aké-Assi (1984). These observations confirm the peculiarity of this forest.
Generally, a forest presenting good wealth, as well as strong rate of species
with particular status such as the endemism, the rarity, deserves a priory
attention for the conservation. This shows the membership this forest in one
of the hotspots of high Guinea that is the south east of Côte d'Ivoire. In fact,
besides the endemism which is considered as an important fact, the rarity holds
an important place in the definition of the species to be kept. The presence of
numerous endemic species and endangered (particular status species) is
broadly a sign of a great biodiversity and a good level of conservation (Adou
Yao & Roussel, 2007).The presence of a Sassandrian in the Tanoé-Ehy Forest
goes with works of Adou Yao (2007). But Guillaumet &Adjanohoun (1971)
68European Scientific Journal July 2018 edition Vol.14, No.21 ISSN: 1857 – 7881 (Print) e - ISSN 1857- 7431
noted the absence of Sassandrian in the trainings degraded by human. Scieng
this result we can say that Tanoé-Ehy Forest is altogether well kept the
presence in the forest Tanoé-Ehy Forest of these species shows that the forest
possesses a big diversity. In fact according to Myers et al. (2000); Tchouto
(2004), the endemic species are the most sensitive to perturbations caused by
human. Then, the risks of extinction are more important at these species
enfeoffed in housing environments one the very particular conditions.
Concerning the biotopes which make up the Tanoé-Ehy Forest, the
analysis of the importance of the species of every biotope showed that certain
species which contribute strongly to the training of the vegetation one member
of species of the red list of the IUCN. These species are mainly run by the
populations resulting from Ghana country which is limited of the Tanoé-Ehy
Forest by the Tanoé river. These observations show that if the flora and the
vegetation of these biotopes are not protected, they will finish by disappear.
Conservation value
Considering conservation values we notice that the swamp forest has
a great value of conservation. This biotope deserved so special attention.
Results similar ones were made by Adou Yao et al. (2005) at the southern
level of the National Park of Tai. It could be activities which have more
negative impact in these biotopes. It is mainly the traces of old farms (tracks,
tree trunks) that testify to these disturbances, major causes of the massive
presence of pioneer species.The observation of the histograms of the profiles
of average coverings of specie realized in the Tanoé -Ehy Forest show that the
histogram of the dry land forest is similar to the type of Chatelain (1996) and
to the H twice of Menzies (2000) characterizing the statements of primaries
forest. This resemblance shows that this biotope would be the best kept
environment.
Conclusion
This study showed that the Tanoé-Ehy Forest, the last forest relic in the
south-eastern of Côte d’Ivoire includes 432 species. Among the species 51
have particular status species. The presence of numerous particular status
species (endemic species and endangered) in this forest is broadly a sign of a
great biodiversity and a good level of conservation. However, these species
are mainly run by the populations resulting from Ghana country and the
populations around this forest there is a composite population made up by the
autochthons, the natives of Tanoé-Ehy areas, the allochthons which are
nationals coming from other regions of Côte d‘Ivoire and foreigners.
Concerning the diversity, the Shannon index showed that the Tanoé-Ehy
Forest is among the most diverse forests of swampy environments in particular
and dense evergreen forests in general. Considering conservation values of the
69European Scientific Journal July 2018 edition Vol.14, No.21 ISSN: 1857 – 7881 (Print) e - ISSN 1857- 7431
biotope we notice that the swamp forest has a great value of conservation.
However, the dry land forest would be the best kept environment.
Finally, we urge for the protection of these forests as they represent an
important refuge for the forest flora in the South-Eastern of the Côte d’Ivoire,
a region where only few forests persisted until today.
Acknowledgments
This work has benefited from funding from the Strategic Support to
Scientific Research Program and the Swiss Center for Scientific Research
through the Research and Action Program for the Safeguarding of Primates
in Côte d'Ivoire. Our thanks also go to the field guides of the region for having
agreed to accompany us on the ground.
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